Many conventional solders contain lead as a major constituent thereof. Such solders often have desirable physical properties, and the use of lead-containing solders is widespread throughout several industries, including those concerned with the production of printed circuit boards. For example, a solder containing a 63% tin and 37% lead is commonly used in wave-soldering processes.
However, there are increasing demands for lead-free solders, due, for example, to environmental considerations, and it seems likely that, within the next few years, it will be a legal requirement in several countries for solders used in the manufacture of many items to contain little or no lead.
Previous attempts to formulate lead-free solders have met with limited success. Conventional lead-free solders generally have undesirable physical properties, including poor wetting properties, low fluidity, poor compatibility with existing component coatings and excessive drossing. A particular problem which has been recognised in the use of lead-free solders is the issue of fillet lifting, where a fillet of solder at the edge of a through-plated hole in a printed circuit board tends to separate from the underlying material, for example, a nickel/gold coating. Another problem is the fact that lead-free solders tend to have a high dissolution rate for copper, so that copper is leached into the lead-free solder from components and circuit boards in contact with the solder.
As a result, some manufacturers are finding that existing soldering processes which have functioned effectively for many years must now be significantly adapted to accommodate the use of lead-free solders. In addition, the existing materials that are employed in the production of printed circuit boards may have to be replaced in order to be compatible with the use of lead-free solders. This adaptation of processes and materials is widely regarded as a poor use of resources, particularly as the standard of articles manufactured using known lead-free solders is, as indicated above, often considerably below that achievable using conventional leaded solders.